The present invention relates to a camera system for acquiring images of scenes with wide angles; for example, omni-directional scenes.
Various camera systems have been proposed to acquire images of scenes with wide angles; for example, hemispherical or omni-directional scenes.
Typical known omni-directional imaging methods have been configured to acquire images of omni-directional scenes by manners of:
(1) arranging a number of cameras radially from a virtual spherical plane, and acquiring images of a scene by the cameras and then synthesizing the acquired images;
(2) rotating a camera around a center axis, and synthesizing images acquired by the camera;
(3) disposing a reflecting mirror composed of a convex mirror having a hyperbolic plane and locating a camera at a second focal point of the hyperbolic plane of the reflecting mirror, and acquiring an image formed on the reflecting mirror by the camera;
(4) disposing a reflecting mirror composed of plane mirrors arranged to form planes of a regular polygonal pyramid and locating cameras at positions opposed to those of the planes of the reflecting mirror, and acquiring images formed on the planes of the reflecting mirror by the cameras and then synthesizing the acquired images.
The above-described omni-directional imaging methods, however, have the following problems:
According to the method (1) characterized by arranging the number of cameras radially from the center of a virtual spherical plane, since the camera system becomes large to occupy an installed location thereof, an imaging position of the camera system is positioned apart from the center of the virtual spherical plane.
As a result, since imaging positions of respective cameras are positioned apart from each other, a parallax occurs among the images acquired by the cameras, wherein there arises a problem that a complicated operation is required to be performed for synthesizing the images acquired by the cameras.
According to the method (2) characterized by rotating the camera, since it takes a certain time to acquire an image of a scene by the rotating camera, it is difficult to acquire an image of a dynamic object.
According to the method (3) characterized by locating the camera at the second focal point of the reflecting mirror having the hyperbolic plane, the camera system is able to acquire an image of a hemispherical or omni-directional scene. However, since only one camera can be disposed at the second focal point of the reflecting mirror, there is a limitation in terms of enhancing a resolution. Such a method, therefore, fails to acquire an image of a hemispherical scene with a high resolution.
According to the method (4) characterized by arranging the number of cameras at positions opposed to those of the plane mirrors forming the regular polygonal pyramid shaped reflecting mirror and acquiring an image formed on the reflecting mirror by the cameras, since light rays are reflected from the plane mirrors, an imaging field of view of the camera system becomes 90xc2x0 or less, with a result that it is insufficient to acquire an image of a hemispherical scene.
Another type of related art camera system of acquiring an image of a hemispherical or omni-direction scene by using fish-eye lenses will be described with reference to FIG. 1. FIG. 1 is a schematic view showing a configuration of the related art camera system using the two fish-eye lenses.
Referring to FIG. 1, there is shown a camera system 50 including a first imaging unit or camera unit 51 having at its leading end a fish-eye lens 61 having an imaging field of view xcex5 and a second imaging unit or camera unit 52 having at its leading end a fish-eye lens 61.
An image acquired by each of the first and second imaging units 51 and 52 through the fish-eye lens 61 having an imaging field of view xcex5 is converted into an image signal in a camera portion 62 provided in each of the first and second imaging units 51 and 52, and the image signal is supplied to a signal synthesizing unit 63 provided at a stage subsequent to the camera system. The image signals supplied from the first and second imaging units 51 and 52 are synthesized by the signal synthesizing unit 63.
In this camera system, the first and second imaging units 51 and 52 are arranged such that imaging directions of the two fish-eye lenses 61 are reversed to each other and the optical axes thereof are aligned in line.
The related art camera system configured as described above, however, has a problem. Since the first and second imaging units 51 and 52 are arranged such that the imaging directions of the two fish-eye lenses 61 are reversed to each other and the optical axes thereof are aligned in line, a distance between the two fish-eye lenses 61 becomes longer, with a result that a dead space impossible to be imaged becomes wider, and a parallax between the images becomes large due to a difference between the positions of the fish-eye lenses 61.
With respect to the above-described related art camera system, there has been known a method in which image signals acquired by the two imaging units or camera units 51 and 52 each having the fish-eye lens 61 are separately recorded by two recorders.
Such a method, however, has a problem that since both the recorders must be operated in synchronization with each other, the configuration of the camera system becomes complicated.
An object of the present invention is to solve the above-described problems and to provide a camera system capable of acquiring an image of a scene with a wide angle, such as an omni-directional scene, as well as acquiring an image of a dynamic object.
To achieve the above object, according to a first embodiment of the present invention, there is provided a camera system including a reflecting mirror, a first imaging unit, and a second imaging unit. The reflecting mirror has a mirror surface disposed around a center axis, wherein the mirror surface is spread on one side of the center axis to form an opening portion. The first imaging unit is provided within a plane composed of an outer surface of the reflecting mirror and a plane extending from the outer surface of the reflecting mirror on the opening portion side. The second imaging unit is disposed opposite to the mirror surface of the reflecting mirror, and includes a number of cameras disposed on the same circumference centered at the center axis of the reflecting mirror in such a manner as to be spaced from each other at equal intervals.
With this configuration, an image of a scene on the opening portion side can be acquired, from the interior of the reflecting mirror, by the first imaging unit, and an image of a scene, formed on the mirror surface of the reflecting mirror, can be acquired by the cameras of the second imaging unit opposed to the mirror surface of the reflecting mirror. In particular, an image of a scene with a wide angle, formed on the reflecting mirror, can be acquired by the second imaging unit.
Since the cameras of the second imaging unit are disposed on the same circumference centered at the center axis of the reflecting mirror in such a manner as to be spaced from each other at equal intervals, the cameras are able to acquire parts of an image formed on the reflecting mirror without occurrence of any deviation due to a parallax among the parts of the image.
To achieve the above object, according to a second embodiment of the present invention, there is provided a camera system capable of acquiring an image of a scene with a wide angle with a simple structure. The camera system includes a first imaging unit having at its leading end a fish-eye lens, and a second imaging unit having at its leading end a fish-eye lens. The first imaging unit and the second imaging unit are arranged adjacent to each other in such a manner that optical axes of the fish-eye lenses of the first and second imaging units are offset from each other in parallel, and imaging directions of the fish-eye lenses of the first and second imaging units are reversed to each other.
With this configuration, since the optical axes of the fish-eye lenses are offset from each other in parallel and the imaging directions thereof are reversed to each other, the first and second imaging units can be disposed adjacent to each other. As a result, it is possible to obtain an image of a scene with a wide angle by acquiring images of halves, spread in the reversed directions, of the scene by the two imaging units and then synthesizing the two images.
Since the optical axes of the fish-eye lenses are offset from each other in parallel and the imaging directions thereof are reversed to each other, the distance between the two fish-eye lenses disposed at both the ends of the two imaging units can be shortened.
Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Invention and the Figures.